The tropical circulation in the Australian/Asian region - November 1987 to April 1988

In this paper a broad summary of the tropical circulation between 70°E and 180°, for the period November 1987 to April 1988, is presented. Analyses of tropospheric flows, sea surface temperatures, tropical cyclone tracks, circulation indices and rainfall data are discussed. The 1987 El Niño-Southern Oscillation (ENSO) warm event was in decline at the beginning of the period and the Southern Oscillation Index (SOI) remained small through the period. Despite this, some of the circulation anomalies associated with the ENSO event persisted well into the season. The monsoon in the southern hemisphere was weaker than normal, resulting in below average rainfall over north Australia. The weakness of the monsoon was also undoubtedly linked to the historically low level of tropical cyclone activity in the southern hemisphere. The monsoon was characterised by low' frequency oscillations in intensity linked to the main weather events. Over India and the Bay of Bengal the northeast monsoon was weaker than normal; in the southeast Asian sector its onset was later than usual and low frequency oscil-lations characterised its intensity. Northeasterly surges and near equatorial vortices, major weather-producing mechanisms over South-East Asia and the South China Sea, were important elements of the monsoon circulation, the occurrence of northeasterly surges being above the long-term mean.